For qualitative and quantitative analysis of target components of biological samples such as blood, urine, or the like, automatic analyzers measure the concentration by adding a reagent to the biological sample and causing the sample to biochemically react with the reagent. Since such automatic analyzers can attain improved reproducibility of measurement results and quick measurement of samples, the automatic analyzers are widely used in large hospitals, inspection centers, and the like. One of the reasons for widespread use is that the automatic analyzer employs a dispensing device capable of automatically dispensing a sample and a reagent with high accuracy at a high speed for their biochemical reaction.
In particular, a probe can be used to capture a predetermined amount of reagent or sample. In this case, variations in the amount of the reagent or the like attached to an outer wall of the probe raises the following: probabilistic carrying in of the reagent or the like to a vessel into which the reagent or the like is dispensed or to a sample vessel for the next time or later; and insufficient cleaning of the outer wall of the probe.
Then, mixing of a reagent with another reagent or mixing of a sample with another sample will lead to an increase in a variation in analysis reproducibility and an increase in cross-contamination between samples.
There is a known method for minimizing the amount of the reagent or the like attached to the outer wall of the probe and a variation in amount of the attached reagent or the like. Such a method causes a sensor to detect a liquid level, and is adapted to control the immersion depth of a probe's top end into the reagent or the sample, thereby performing dispensing with high accuracy at a high speed.
For example, an example is known in which a dispensing probe is used as one electrode for detecting a liquid level, the other electrode is used as a vessel holding stage, and the liquid level within a vessel is detected on the basis of a variation in capacitance between the electrodes. Examples of the known example include a device that uses a bridge circuit (Patent Document 1) and a device that uses a differentiating circuit (Patent Document 2).
Each of the examples described above adopts a system in which an input signal with a certain frequency component is applied to the dispensing probe.
As an example of a device capable of performing dispensing at a high speed, a high-performance analyzer (Patent Document 3) is known which has a plurality of probes and causes the plurality of probes to simultaneously dispense a reagent, thereby making it possible to perform simultaneous processing per unit time.
In addition, there is known an automatic analyzer which holds many types of reagents stored in many containers on a single reagent disk and is capable of measuring several tens of types of target components at one time (Patent Document 4).